Erase and reinstall Mac OS X Lion
You can erase your computer using Disk Utility and then reinstall Mac OS X. Before you erase and reinstall, back up your essential files. If you’re installing on a portable computer, make sure your power adapter is connected and plugged in.
Important: To reinstall Mac OS X, you need to be connected to the Internet.
- Choose Apple menu > Restart, and then hold down the Command (⌘) and R keys while the computer restarts.
- Select “Disk Utility,” and then click Continue.
- Select your startup disk from the list on the left, and then click the Erase tab.
- From the Format pop-up menu, select Mac OS Extended (Journaled), type a name for your disk, and then click Erase.
- After the disk has been erased, choose Disk Utility > Quit Disk Utility.
- If you’re not connected to the Internet, choose a network from the Wi-Fi menu in the right corner of the menu bar (in the top-right corner of the screen).
- Select Reinstall Mac OS X, click Continue, and then follow the instructions.